Color print simulator



SEAR C r1 SUSHI Nov. 2, 1965 J- G. JORDAN COLOR PRINT SIMULATOR FiledNov. :50, 1961 INVENTOR. JOSEPH. G. JORDAN hll A TTOR/VEYS United StatesPatent York Filed Nov. 30, 1961, Ser. No. 156,006 7 Claims. (Cl. 88-1)This invention relates to devices for analyzing the various color imageson the separation image-bearing elements used in a multicolor printingprocess and, more particularly, to a new and improved device foranalyzing such images to produce a visual representation of the resultswhich will be obtained when they are combined in a print.

In multicolor printing processes, separate image-bearing elements suchas continuous tone negative or positive transparencies are made in anyof several ways as, for example, by photographing the objectsuccessively through different colored optical filters so that each ofthe elements contains the image information relating to only one of thevarious colors. From these elements, halftone plates or cylinders aremade by a process which may involve many complex and time-consumingsteps and it is impossible to ascertain what the final print will looklike until these plates have been made and used to produce a proof. Oncethe process has been completed and the plates are made, however, theoptimum point for introducing corrections into the separation images haspassed and any necessary changes must then be made by hand on theengraved plates where the letterpress process is used, or, in the offsetprocess, the plates must be made over, while, in gravure, the cylindersmust be re-etched.

Various attempts have been made heretofore to predict the appearance ofthe proof or final print from the separation images at an earlier stageof the process, such as by substituting a simpler photographic processin place of the plate making and printing process or by photoelectricanalysis of the various separation images point by point and, synthesisof a corresponding proof based upon an empirically determinedrelationship between the separations and a resulting print. In theformer case, the absence of any photographic dyes or colorantssufliciently similar to printing ink makes the resulting approximationof the final print inaccurate while, in the latter case, the requiredmachinery is complex and expensive.

Accordingly, it is an object of the present invention to provide a newand improved device for simulating accurately the appearance of a colorprint from separation images which avoids the above-mentioneddisadvantages of the prior art.

Another object of the invention is to provide a new and improved colorprint simulator capable of synthesizing an accurate representation of acolor print immediately and directly from color separation image-bearingelements without requiring any further processing of the images.

A further object of the invention is to provide a'new and improvedcoloeprwlator of the above character which is simple and inexpensive instructure and operation.

These and other objects of the invention are attained by dividing lightfrom a source into two color components corresponding respectively tothe reflection and absorption characteristics of one of the inks to beused in the printing process, projecting one of these components througha corresponding separation image-bearing element, recombining the colorcomponents, and then subjecting the combined light to similar successiveoperations involving each of the other separation image-bearingelements. The resulting image, which has been color modified in thismanner may be viewed directly or projected onto a screen for viewing. Ina particular device for carrying out the invention, dichroic mirrors areutilized to divide the light into color components corresponding to thereflection and absorption characteristics of the corresponding printinginks. Alternatively, optical color filters having the samecharacteristics may be used.

Further objects and advantages of the invention will be apparent from areading of the following description in conjunction with theaccompanying drawings in which:

FIG. 1 is a schematic view of a typical color print simulator arrangedaccording to the invention;

FIG. 2 is a schematic view showing the arrangement of one form of lightdivider suitable for use in the system shown in FIG. 1, and;

FIG. 3 is a schematic diagram illustrating the relative dimensions of aportion of a simulator utilizing the light divider arrangement shown inFIG. 2.

In the representative embodiment of the color print simulator shown inFIG. 1, the images on three color separation positive transparenices 10,11, and 12 and a black printer positive transparency 13, from whichprinting plates or cylinders are to be made, are synthesized to projecta color image accurately representing the appearance of the print whichwill be produced from the plates or cylinders onto a screen 14. To thisend a conventional condensing lens 15 concentrates light from a source16 through the black printer 13 onto an objective lens 17, which is thefirst imaging element of the system.

It will be understood of course, that if no black printer is used in theprocess, the element 13 is omitted from the system. Moreover, thetransparencies 10-13 may be of either continuous tone images, as isusually the case in the gravure process, or halftone images as used inthe offset process, for example. Also, although the simulator isdescribed herein with reference to processes for preparing plates andcylinders for press printing, it will be understood that the inventionis equally applicable to photographic or other processes wherein colorprints are made from color separation images.

In accordance with the invention, the print simulator includes means fordividing light from the lens 17 into two components, one of whichcorresponds in color to the light absorbed by one of the printing inksused in the process and the other of which corresponds in color to thelight reflected by the same ink. In the illustrated embodiment of theinvention, this light dividing means comprises a dichroic mirror 18which transmits a beam 19 of light having a particular spectralcharacteristic and reflects a beam 20 having a difierent spectralcharacteristic. Assuming the transparency 10 is the one from which ayellow ink printing plate is to be made, the dichroic mirror 18 has aspectral reflection distribution similar to the spectral absorptiondistribution of the yellow ink while its transmittance distribution islike the spectral reflection distribution of the yellow ink.Alternatively, if desired, the dichroic mirror 18 may be replaced by ahalf-silvered mirror and optical color filters having the requiredspectral transmittance characteristics may be interposed in the paths ofthe reflected and transmitted beams of light, but with this arrangement,a light source of considerably higher intensity must be used to obtainthe same illuminance on the screen 14.

After being reflected by a mirror 21, the beam 20 passes through a fieldlens 22 which, in conjunction with the objective lens 17, superimposesan image of the black printer positive transparency 13 on the yellowseparation positive 10 so that corresponding image portions coincide. Inthis way, the yellow separation positive absorbs light of the samespectral character and to the same extent at each point in the image aswill be absorbed by the yellow ink in a print made from the separationimage.

At the same time, the beam 19 transmitted by the dichroic mirror 18 andrepresenting light of the quality which is reflected by the yellow inkpasses through a field lens 23 identical to the lens 22 so that acorresponding aerial image 24'of the black printer 13 is formed. Thislight beam is then reflected by a mirror 25 and by a half-silveredmirror 26 which also transmits light in the beam 20 passed by the yellowtransparency 10 so as to form a combined beam of light 27 wherein theyellow ink absorption information has been subtracted from the originallight. Moreover, inasmuch as the light absorbed by a colored material isgenerally the color complement of the light reflected by the material, apositive complementary image-bearing color separation transparency (notshown) which has been made from the original object through acomplementary color filter may, if desired, be interposed in the beam 19to coincide with the aerial image 24 instead of the transparency 10 inthe beam 20. V

In a similar manner the beam 27, after passing through an objective lens28, is divided by a dichroic mirror 29 selected to have a spectralreflectance characteristic similar to the absorption characteristic ofthe magenta printing ink used in the process and a tranmittancecharacteristic like the spectral reflectance of that ink, the separationtransparency 11 being the one from which the magenta printing plate isto be made. The reflected beam 31, after further reflection by a mirror32, passes through a field lens 33 which, with the objective lens 28,superimposes the combined aerial image 24 and yellow separation image inthe transparency 10 on the magenta separation positive 11 coincidentwith the image thereon, while the transmitted beam passes through afield lens 34 to form an aerial image 35 of the combined images 10 and24. After reflection by a further mirror 36, the beam 30 is recombinedwith the beam 31 by a half-silvered mirror 37 to form a beam 38 whereinboth the yellow and the magenta ink absorption information have beensubtracted.

This combined beam 38 is likewise transmitted through an objective lens39 and divided by a dichroic mirror 40 which passes a beam 41 having thecyan ink reflectance characteristic and reflects a beam 42 having thecyan ink absorption characteristic the latter beam being furtherreflected by a mirror 43 and imaged by a field lens 44 onto thecyan-separation positive 12. As in the preceding stages, the transmittedbeam 41 is imaged by a field lens 45 to form an aerial image 46 and thendeflected by a mirror 47 to a half-silvered mirror 48 which recombinesthe two beams. From this point, a projection lens 49 projects therecombined light onto the screen 14 to form an image which has the samecolor characteristics as the ultimate print will have. If desired, thescreen 14 may be omitted and the lens 49 may be selected to permit aviewer to observe the combined image by looking toward the half-silveredmirror 48.

Although the image produced in the manner described above will representreasonably accurately the color characteristics of a print made from theseparation positive, its appearance will difier slightly from the actualprint in certain respects. For example, the simulator does not makeallowance for the changes in the halftone dot size effected in the platemaking and printing processes or for the nonuniformity of ink filmthickness across the dots, nor can it simulate the effect of inktrapping variations in printing or internal light scattering in thepaper. Certain of these effects may, however, be introduced into thepresent system by conventional optical techniques, such as by varyingthe focus of the images on the separation elements, introducing flare ornon-image-forming light into certain of the beams, 01'

making the spectral characteristics of the dichroic filters slightlydifierent from those of the inks used in the process.

In order to produce a field of uniform color in the beams transmittedand reflected by a dichroic mirror, all of the light must be incidentupon the mirror at approximately the same angle. To accomplish this inthe present system, the objective lenses 17, 28, and 39 which areschematically shown in FIG. 1, are preferably of the telecentric formshown in FIG. 2, having a positive component 50 and two negativecomponents 51 and 52, one for each emergent beam, the correspondingdichroic mirror 53 being located between the positive and negativecomponents. This objective also includes an aperture stop 54 located infront of the positive component 50 adistance equal to the focal lengthof that element so that the principle rays from all points in the fieldof view emerge from the positive lens element in parallel directions sothat they all strike the dichroic mirror 53 at the same angle. Althoughall the other rays from each point in the object have an angulardistribution about the principal ray, this distribution will be the samefor all parts of the field so that the color of the field in each of thedivided beams is uniform throughout.

While this result might be accomplished by using a positive lens elementalone, for one-to-one magnification this would require a dichroic mirror53 larger than the object. Accordingly, the negative elements 51 and 52are included to increase the focal length of the system so that thepositive element contributes relatively lower magnification and can beproportionately smaller. Another advantage of the telecentric objectiveis that, if the negative and positive components have the same numericalfocal length, the addition of the negative component makes the objectiveof a form that is inherently free of astigmatism and field curvature.

In the schematic diagram shown in FIG. 3 the relative dimensions of aportion of a simulator utilizing a particular form. of telecentricobjective are illustrated. In this case, the positive and negativecomponents 50 and 51 have a focal length of two units of length, such asinches, and are one unit in diameter and they are separated by one unitof distance. The aperture stop 54, which is two units distant from thepositive element, preferably has an opening one-fifth unit in diameterso that one-to-one magnification with full field coverage is obtainedfor an object 55 having a maximum dimension of three units and locatedten units away from the positive lens element.

Although the invention has been described herein with reference tospecific embodiments, many modifications and variations therein willreadily occur to those skilled in the art. Accordingly, all suchvariations and modifications are included within the intended scope ofthe 'invention as defined by the following claims.

I claim:

1. A device for simulating the appearance of a color print from aplurality of transparent color separation image-bearing elements eachcorresponding to one of a corresponding plurality of colored materialsfrom which the color print is to be made comprising light source means,first light modulating means comprising light dividing means disposed ata first location for dividing light into two beams which followdifferent paths to a second location, one of which has a colorcharacteristic approximately the same as that of light reflected by thecorresponding colored material and the other of which has a colorcharacteristic approximately the same as that of light absorbed by thecorresponding colored material, a corresponding color separationimage-bearing element interposed in the path of one of the two beamsbetween the first and second location, and means disposed at the secondlocation for recombining the two beams of light into a single beam,second light modulating means comprising light dividing means disposedat a third location for dividing light received from the second locationinto two beams which follow different paths to a fourth location, one ofwhich has a color characteristic approximately the same as that of lightreflected by a second corresponding colored material different from thecolored material of the first light modulating means, and the other ofwhich has a color characteristic approximately the same as that of lightabsorbed by the second corresponding colored material, a secondcorresponding color separation image-bearing element interposed in thepath of one of the two beams between the third and fourth locations, andmeans disposed at the fourth location for recombining the two beams oflight into a single beam whereby the appearance of a simulated colorprint can be previewed.

2. A device according to claim 1 wherein the corresponding colorseparation image-bearing element interposed in one of the two beams ofthe first and second light modulating means comprises means forsupporting a corresponding positive transparency in the beam having acolor characteristic approximately the same as that of light absorbed bythe corresponding colored material.

3. A device according to claim 1 wherein each light dividing meanscomprises a dichroic mirror.

4. A device according to claim 3 including objective lens meanscomprising a positive lens element interposed in the light beam incidenton the dichroic mirror of each modulating means to project all theprincipal rays toward the mirror in substanttially parallel directionsand a negative lens element in each of the beams reflected andtransmitted by the dichroic mirror.

5. A device according to claim 4 wherein the positive and negative lenselements have the same focal length and including aperture stop meansinterposed a distance equal to the focal length in front of the positivelens element.

6. A device according to claim 1 including a transparent black printerimage-bearing element interposed in the path of light from the source.

7. In a process for simulating the appearance of a color print from aplurality of transparent color-separation image-bearing elements eachcorresponding to one of a corresponding plurality of colored materialsfrom which the color print is to be made, the steps of dividing a beamof light at a first location into two beams which follow dilferent pathsto a second location, one of which has a color characteristicapproximately the same as that of light reflected by the correspondingcolored material and the other of which has a color characteristicapproximately the same as that of light absorbed by the correspondingcolored material, transmitting one of the beams through a correspondingcolor separation imagebearing element located in the path of the beambetween the first and second locations, recombining the two beams oflight into a single beam at the second location, dividing the beam fromthe second location at a third location into two beams which followdifierent paths to a fourth location, one of which has a colorcharacteristic approximately the same as that of light reflected by asecond corresponding colored material different from that of thefirst-mentioned colored material and the other of which has a colorcharacteristic approximately the same as that of light absorbed by thesecond corresponding colored material, transmitting one of the beamsthrough a corresponding color separation image-bearing element locatedin the path of the beam between the third and fourth locations, andrecombining the two beams of light at the fourth location whereby theappearance of a simulated color print can be previewed.

References Cited by the Examiner UNITED STATES PATENTS 2,961,920 1 1/60Sachtleben 88-24 2,976,348 3/61 Bailey et al. 88-24 2,981,791 4/61 Dixon88-24 2,983,824 5/61 Weeks et a1 88-1 2,985,065 5 61 Haynes et al. 88-243,019,703 2/62 Kilminster 8824 JEWELL H. PEDERSEN, Primary Examiner.

WILLIAM MISIEK, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.5,215,030 November 2, 1965 Joseph G. Jordan It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 5, lines 20 and 21, strike out "means for supporting a"; line 30,for "substanttially" read substantially --c Signed and sealed this 23rdday of August 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A DEVICE FOR SIMULATING THE APPEARANCE OF A COLOR PRINT FROM APLURALITY OF TRANSPARENT COLOR SEPARATION IMAGE-BEARING ELEMENTS EACHCORRESPONDING TO ONE OF A CORRESPONDING PLURALITY OF COLORED MATERIALSFROM WHICH THE COLOR PRINT IS TO BE MADE COMPRISING LIGHT SOURCE MEANS,FIRST LIGHT MODULATING MEANS COMPRISING LIGHT DIVIDING MEANS DISPOSED ATA FIRST LOCATION FOR DIVIDING LIGHT INTO TWO BEAMS WHICH FOLLOWDIFFERENT PATHS TO A SECOND LOCATION, ONE OF WHICH HAS A COLORCHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHT REFLECTED BY THECORRESPONDING COLORED MATERIAL AND THE OTHER OF WHICH HAS A COLORCHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHT ABSORBED BY THECORRESPONDING COLORED MATERIAL, A CORRESPONDING COLOR SEPARATIONIMAGE-BEARING ELEMENT INTERPOSED IN THE PATH OF ONE OF THE TWO BEAMSBETWEEN THE FIRST AND SECOND LOCATION, AND MEANS DISPOSED AT THE SECONDLOCATION FOR RECOMBINING THE TWO BEAMS OF LIGHT INTO A SINGLE BEAM,SECOND LIGHT MODULATING MEANS COMPRISING LIGHT DIVIDING MEANS DISPOSEDAT A THIRD LOCATION FOR DIVIDING LIGHT RECEIVED FROM THE SECOND LOCATIONINTO TWO BEAMS WHICH FOLLOW DIFFERENT PATHS TO A FOURTH LOCATION, ONE OFWHICH HAS A COLOR CHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHTREFLECTED BY A SECOND CORRESPONDING COLORED MATERIAL DIFFERENT FROM THECOLORED MATERIAL OF THE FIRST LIGH TMODULATING MEANS, AND THE OTHER OFWHICH HAS A COLOR CHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHTABSORBED BY THE SECOND CORRESPONDING COLORED MATERIAL, A SECONDCORRESPONDING COLOR SEPARATION IMAGE-BEARING ELEMENT INTERPOSED IN THEPATH OF ONE OF THE TWO BEAMS BETWEEN THE THIRD AND FOURTH LOCATIONS, ANDMEANS DISPOSED AT THE FOURTH LOCATION FOR RECOMBINING THE TWO BEAMS OFLIGHT INTO A SINGLE BEAM WHEREBY THE APPERANCE OF A SIMULATED COLORPRINT BE PREVIEWED.